Laser Enhanced Wet Chemical Etching of Single Crystalline Silicon

Abstract

Laser enhanced wet etching of single crystalline silicon has been investigated. In this report, KOH and NH₄HF₂ has been tested as etchant to discuss possibility of chemical drilling of silicon enhanced by laser beam transmitted through optical fibers. As a result of CW Nd:YAG laser irradiation in KOH, the entire silicon surface including the area out of the laser spot was corroded. H₂O₂ was accordingly added to the solution to realize local selective drilling. Suitable concentration of KOH depends on H₂O₂ concentration, laser power and dopant type. The fact suggests that composition optimization will make the etchant applicable to drilling with optical fibers. In case of NH₄HF₂ laser enhanced etching, the etch rate matched with the rate of KOH and H₂O₂. However, ideas of protecting silica optical fiber from NH₄HF₂ should be necessary for achievement of drilling with fibers because high laser power which must damage plastic optical fiber is required for enough etch rate.